This invention relates to apparatus for dampening the recoil of percussion tools of the type having a reciprocating tool bit insertable in a feeding sleeve attached to (or forming part of) a tool housing. A pressure medium intermittently actuates a hammer piston which delivers blows to the tool bit, while a tool feeding force is applied to the tool housing.
In conventional rock boring machines spring arrangements are provided for dampening the tool recoil. In this manner, the recoil is absorbed preponderantly by the feeding force and consequently, the operating person or the feed carriage (mount) has to absorb the impacts.
German Pat. No. 2,610,910 discloses a method according to which the tool feeding force and/or the pressure in the dampening chamber is set in relation to the magnitude of the recoil forces in such a manner that the dampening piston and the tool bit feeding sleeve do not, during reciprocation, abut the tool housing. The dampening chamber is continuously charged with the pressurized fluid with the interposition of a pressure setting arrangement.
The embodiment disclosed in the above-noted patent includes a feed sleeve for the boring tool. The sleeve has a hollow cylindrical extension in the zone of the piston rod which constitutes the hammer and an enlargement which constitutes a dampening piston and which is situated between an inner wall formed by a sleeve guiding the piston rod and an outer wall formed by the wall of the tool housing. In the dampening chamber defined in this manner, pressurized fluid is introduced with the intermediary of a settable reduction valve and a check valve.
By means of the above-outlined conventional arrangement an air cushion is formed between the feeding sleeve that takes up the recoil of the work tool and the tool housing. Each recoil effects a polytropic compression of the air cushion.
If the tool feed is applied by human force, the latter may vary between 0 and 80 kg and thus the pressure in the dampening chamber has to be adapted accordingly. Such an adaptation is not feasible with the above-described conventional system. Although that system includes a setting member, the latter, however, is not adapted to be set every time the pressure force changes. It is further apparent that for a satisfactory dampening effect the pressure in the dampening chamber has to be maintained at the lowest possible level which, however, should be sufficiently high to prevent the recoil from causing any contacting between the dampening piston and the tool housing.